Method of allocating IP address of image forming apparatus using DHCP, image forming apparatus and system of allocating IP address using DHCP

ABSTRACT

A method of allocating an IP address of an image forming apparatus using Dynamic Host Configuration Protocol (DHCP), and an image forming apparatus and system performing the method, the method including requesting a DHCP server to allocate an IP address to an image forming apparatus having a previously allocated IP address in response to the image forming apparatus being re-connected to a network, responding to the IP address allocation request by the DHCP server, declining to respond to the response of the DHCP server, and providing the previously allocated IP address to the image forming apparatus upon receiving no response from the image forming apparatus after a predetermined time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of prior application Ser.No. 12/544,397, filed on Aug. 20, 2009 in the United States Patent andTrademark Office, which claims the benefit under 35 U.S.C. §119(a) ofKorean Patent Application No. 10-2008-0096213, filed on Sep. 30, 2008,in the Korean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

1. Field of the Invention

The present general inventive concept relates to allocation of anInternet protocol (IP) address, and, more particularly, to a method ofallocating an IP address of an image forming apparatus using the DynamicHost Configuration Protocol (DHCP), an image forming apparatus to whichan IP address is allocated using DHCP, and a system of allocating an IPaddress using DHCP.

2. Description of the Related Art

In general, a Dynamic Host Configuration Protocol (DHCP) server has afunction of transmitting configuration parameters to a plurality ofhosts using Transmission Control Protocol/Internet Protocol (TCP/IP).The DHCP allows a client to receive dynamic or static IP configurationinformation from the DHCP server when booted so that there is no needfor a network manager to configure a network for each host, andallocates a number of IP addresses, which is smaller than the number ofactually existing clients, so that a limited number of IP addresses canbe efficiently used.

In the case of dynamic allocation of an IP address, when a configurationinformation request is received from a client, the network managerselects an IP address that is not currently allocated to any client froma predetermined range of predetermined IP addresses (for example,100.1.1.1 through 100.1.1.254) and allocates the selected IP address tothe client. Here, the DHCP server does not grant the client a right touse the IP address unlimitedly, but gives the client a right to use theIP address only for a predetermined period previously set by the networkmanager.

In the case of static allocation of an IP address, when a configurationinformation request is received from a client, the DHCP server confirmswhether the hardware address of the client is included in a tableconstructed of pairs of IP addresses previously designated by thenetwork manager and hardware addresses and allows the client to use IPconfiguration information unlimitedly only when the table includes thehardware address of the client.

When a network printing device, constituting a DHCP client, is turnedoff/on, the network printing device operates and requests the DHCPserver to allocate an IP address thereto. In this situation, the DHCPserver allocates an IP address other than the IP address previouslyallocated to the DHCP client to the DHCP client. This affects an IPaddress based network printing service. That is, even if a user simplyturns off/on the network printing device, IP address configuration ischanged and thus the user cannot use a desired service or has toreconfigure the IP address of the network printing device.

SUMMARY

The present general inventive concept provides a method of allocating anIP address of an image forming apparatus using Dynamic HostConfiguration Protocol (DHCP) to allocate a previously allocated IPaddress without changing the IP address in response to a DHCP serverallocating a new IP address.

The present general inventive concept also provides an image formingapparatus allocated an IP address using DHCP.

The present general inventive concept also provides an IP addressallocation system in which the image forming apparatus operates as aDHCP client.

Additional aspects and utilities of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

The foregoing and/or other features and utilities of the present generalinventive concept may be achieved by providing a method of allocating anIP address of an image forming apparatus using DHCP, which includesrequesting a DHCP server to allocate an IP address to an image formingapparatus having a previously allocated IP address wherein therequesting is performed by the image forming apparatus, in response tothe image forming apparatus being re-connected to a network; respondingto the IP address allocation request wherein the responding is performedby the DHCP server; declining to respond to the response of the DHCPserver wherein the declining is performed by the image formingapparatus; and providing the previously allocated IP address to theimage forming apparatus wherein the providing is performed by the DHCPserver, upon receiving no response from the image forming apparatusafter a predetermined time.

The foregoing and/or other features and utilities of the present generalinventive concept may also be achieved by providing an image formingapparatus including a storage unit to store an IP address previouslyallocated by a DHCP server, a network interface to transmit/receivepackets to/from the DHCP server used in IP address allocation through anetwork and a controller to request the DHCP server to allocate an IPaddress through the network interface in response to the image formingapparatus being re-connected to the network, receive a packet to confirmwhether the image forming apparatus is connected to the network from theDHCP server through the network interface, decline to respond to thereceived packet, receive the previously allocated IP address transmittedfrom the DHCP server through the network interface and store thereceived IP address in the storage unit.

The foregoing and/or other features and utilities of the present generalinventive concept may also be achieved by providing an IP allocationsystem using DHCP, which includes an image forming apparatus to operateas a DHCP client, a network managed by at least one DHCP server whereinthe at least one DHCP server allocates an IP address to at least oneDHCP client including the image forming apparatus through the networkusing DHCP. The image forming apparatus may include a storage unit tostore an IP address previously allocated by the DHCP server, a networkinterface to transmit/receive packets to/from the DHCP server used in IPallocation through a network and a controller to request the DHCP serverto allocate an IP address through the network interface in response tothe image forming apparatus being re-connected to the network, receive apacket to confirm whether the image forming apparatus is connected tothe network from the DHCP server through the network interface, declineto respond to the received packet, receive the previously allocated IPaddress transmitted from the DHCP server through the network interfaceand store the received IP address in the storage unit. The DHCP servermay include a server storage unit to store a range of IP addresses to beallocated to DHCP clients and a lease list including IP addresses thathave been allocated to the DHCP clients and MAC addresses of the DHCPclients, which correspond to the IP addresses, a server networkinterface to transmit/receive packets to/from the DHCP clients used inIP allocation through the network and a controller to receive the IPaddress allocation request from the image forming apparatus through theserver network interface, transmit the packet to confirm whether theimage forming apparatus is connected to the network to the image formingapparatus, read the previously allocated IP address of the image formingapparatus from the server storage unit upon receiving no response fromthe image forming apparatus to the confirmation packet after apredetermined time and transmit the read previously allocated IP addressto the image forming apparatus.

The foregoing and/or other features and utilities of the present generalinventive concept may also be achieved by providing a method ofallocating an IP address using DHCP, the method including sending an IPaddress allocation request from a device to a DHCP server, sending aconfirmation request from the DHCP server to the device, and providing apreviously allocated IP address to the device by the DHCP server inresponse to not receiving a response to the confirmation request fromthe device.

The foregoing and/or other features and utilities of the present generalinventive concept may also be achieved by providing a device to beallocated an IP address, including a request circuit to request an IPaddress allocation from a server, and a response control circuit todetermine whether to respond to a confirmation request from the server,wherein the response control circuit selectively declines to respond tothe confirmation request in order to be allocated a previously allocatedIP address.

The foregoing and/or other features and utilities of the present generalinventive concept may also be achieved by providing a device to allocatean IP address, including a transmission circuit to transmit aconfirmation request to a client in response to receiving an IP addressallocation request from the client, and an allocation circuit toallocate a previously allocated IP address to the client upon receivingno response from the client after a predetermined time.

The foregoing and/or other features and utilities of the present generalinventive concept may also be achieved by providing an input circuit toselect whether to obtain a new IP address or a previously allocated IPaddress after being reconnected to a network, and a response controlcircuit to decline responding to a confirmation request from a server inresponse to a selection to obtain the previously allocated IP address.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other features and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 illustrates standard procedures (RFC2131) of a Dynamic HostConfiguration Protocol (DHCP) IP address allocating method;

FIG. 2 (a) illustrates a normal operation performed between a DHCPclient and a DHCP server in a DHCP discover procedure;

FIG. 2 (b) illustrates an operation in which the DHCP server confirmsthe DHCP client through Address Resolution Protocol (ARP) packettransmission corresponding to non-standard procedures;

FIG. 2 (c) illustrates a response of the DHCP client to a confirmationoperation of the DHCP server;

FIG. 3 is a block diagram illustrating a configuration of an imageforming apparatus allocated an IP address using DHCP, according to anembodiment of the present general inventive concept;

FIG. 4 illustrates an exemplary allocation mode selecting window used toselect a user allocation mode provided by a user interface;

FIG. 5 is a schematic diagram illustrating an IP allocation system usingDHCP, according to an embodiment of the present general inventiveconcept; and

FIG. 6 is a flowchart illustrating a method of allocating an IP addressto a DHCP client, according to an embodiment of the present generalinventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to various exemplary embodiments ofthe present general inventive concept, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tothe like elements throughout. The embodiments are described below inorder to explain the present general inventive concept by referring tothe figures.

In general, a Dynamic Host Configuration Protocol (DHCP) IP allocatingmethod may be performed according to standard procedures (RFC2131)illustrated in FIG. 1. Referring to FIG. 1, when a DHCP client transmitsa DHCPDISCOVER broadcast packet, a DHCP server may receive theDHCPDISCOVER broadcast packet and transmit a DHCPOFFER to the DHCPclient to provide an IP address usable by the DHCP client. Subsequently,the DHCP client may receive the DHCPOFFER and transmit a DHCPREQUESTthat requests the DHCP server to lease the IP address provided by theDHCP server. The DHCP server may receive the DHCPREQEUST and transmit aDHCPACK to the DHCP client to officially grant the DHCP client the leaseof the IP address. When the DHCP client requests the DHCP server toextend the lease before the lease expires, the DHCP server may transmitan acknowledgement and grant the lease of the IP address to be extendedto the DHCP client.

The transmission of the DHCPOFFER from the DHCP server to the DHCPclient will now be explained in more detail with reference to FIG. 1.According to the present general inventive concept, the DHCP server mayperform a “selecting” operation to select the IP address to be allocatedto the DHCP client. While performing such a procedure, the DHCP servermay confirm whether the DHCP client responds using information regardingthe client that was previously allocated an IP address, which is storedin the DHCP server.

In this operation, the DHCP server may confirm whether the client sendsa response using an ARP broadcast, Internet Control Message Protocol(ICMP), or PING.

However, the conventional DHCP server typically merely confirms therange of IP addresses that can be allocated to the DHCP client in theDHCPOFFER operation and allocates an IP address other than thepreviously allocated IP address to the DHCP client, and thus the IPaddress of the DHCP client is changed.

Although the DHCP server operates based on a vendor specification of theDHCP server, which is included in necessary operations of the standardprocedures (RFC2131), in this conventional case, the IP address of theDHCP client is typically changed when the DHCP client wants to bere-allocated the IP address thereof due to disconnection from the DHCPserver.

Furthermore, the conventional DHCP server included in a wired/wirelesssmall IP sharer or a wireless sharer may perform an operation ofchanging an IP address as described above.

FIG. 2( a) illustrates a typical operation in which the conventionalDHCP server transmits the DHCPOFFER including an IP address to beallocated to the DHCP client to the DHCP client in response to the DHCPclient transmitting the DHCODISCOVER broadcast packet to the DHCPserver. Referring to FIG. 2( b), the DHCP server may perform theselecting operation to confirm an IP address allocatable to the DHCPclient. That is, the DHCP server may send the ARP packet to determinewhether the DHCP client exists. In this situation, the DHCP client maytransmit a response to the ARP packet, as illustrated in FIG. 2( c), andthe DHCP server may allocate a new IP address to the DHCP client. Thatis, the DHCP server does not transmit the IP address previouslyallocated to the DHCP client, but selects a new IP address from therange of IP addresses and transmits the selected IP address to the DHCPclient through the DHCPOFFER. Accordingly, the IP address of the DHCPclient is changed.

To prevent the IP address of the DHCP client from being changed, or frombeing assigned a different IP address than previously allocated, thepresent general inventive concept may decline, in other words refuse, torespond to the ARP packet before the DHCPOFFER operation.

FIG. 3 is a block diagram illustrating a configuration of an imageforming apparatus 300 allocated an IP address using DHCP, according toan embodiment of the present inventive concept. Referring to FIG. 3, theimage forming apparatus 300 according to the present embodiment mayinclude a controller 305, a network interface 310 and a storage unit315. The image forming apparatus 300 may further include a userinterface 320.

The storage unit 315 may store an IP address previously allocated by aDHCP server 350. The network interface 310 may transmit/receive packetsto/from the DHCP server 350 through a network to achieve IP addressallocation.

The controller 305 may request the DHCP server 350 to allocate an IPaddress through the network interface 310 in response to the imageforming apparatus 300 being re-connected to the network. When the DHCPserver 350 transmits a packet to confirm whether the image formingapparatus 300 is connected to the network to the image forming apparatus300, the controller 305 may receive the packet through the networkinterface 310 and may refuse to respond to the received confirmationpacket. In the situation in which the controller 305 controls the imageforming apparatus 300 so as not to respond to the received confirmationpacket, the DHCP server 350 may transmit an IP address that waspreviously allocated to the image forming apparatus 300 based oninformation included in the IP address allocation request alreadyreceived from the image forming apparatus 300. The DHCP server 350 maytransmit this previously allocated IP address to the image formingapparatus 300 after not receiving a response to the confirmation packetafter a predetermined length of time. When the previously allocated IPaddress is transmitted from the DHCP server 350, the controller 305 mayreceive the previously allocated IP address through the networkinterface 310 and may store the received IP address in the storage unit315. The network re-connection can be achieved in response to the imageforming apparatus 300 being turned off and on and the network beingdisconnected and re-connected between the image forming apparatus 300and the DHCP server 350. It may be confirmed that the image formingapparatus 300 is connected to the network using an ARP Broadcast, ICMP,PING, etc.

The user interface 320 may provide an IP allocation mode of selectingwhether the previously allocated IP is maintained in the IP allocationprocess using the DHCP server 350 to a user. FIG. 4 illustrates anexemplary allocation mode selecting window used to select the IPallocation mode provided by the user interface 320. The IP allocationmode may include a new IP allocation mode used to reply to a response ofthe DHCP server 350 to be allocated a new IP address and a previous IPmaintenance mode used to make no reply to the response of the DHCPserver 350 to maintain a previously allocated IP address. The allocationmode selecting window 400 of FIG. 4 is one example configuration used topresent such alternative IP address allocation modes of operation to theuser.

The image forming apparatus 300 may receive the previously allocated IPaddress provided by the DHCP server 350 and store the received IPaddress in the storage unit 315 as a new IP address. The image formingapparatus 300 can receive a response transmitted from the DHCP server350 and display the received response to the user. It may be preferableto display the response through a panel of the image forming apparatus300 or a user interface of a host computer 340 connected to the imageforming apparatus 300.

FIG. 5 is a schematic diagram illustrating an IP allocation system usingDHCP, according to an embodiment of the present general inventiveconcept. Referring to FIG. 5, the IP allocation system according to thepresent embodiment may include an image forming apparatus 500, a network530 and at least one DHCP server 550.

The image forming apparatus 500 may operate as a DHCP client, and mayinclude a user interface 505, a controller 510, a network interface 520,and a storage unit 550. The image forming apparatus 500 may besubstantially similar to the image forming apparatus 300 illustrated inFIG. 3, and thus a detailed explanation thereof is not repeated.

The network 530 may be managed by the at least one DHCP server 550.

The DHCP server 550 may allocate an IP address to at least one DHCPclient including the image forming apparatus 500 through the network 530using DHCP.

The DHCP server 550 may include a server storage unit 560, a servernetwork interface 555 and a server controller 565. The server storageunit 560 may store a range of IP addresses to be allocated to DHCPclients and a lease list including IP addresses that were previouslyallocated to the DHCP clients and MAC addresses of the DHCP clients.

The server network interface 555 may transmit/receive packets to/fromthe image forming apparatus 500 in order to allocate an IP address tothe image forming apparatus 500 through the network 530.

The server controller 565 may receive an IP address allocation requesttransmitted from the image forming apparatus 500 through the servernetwork interface 555 and may transmit a packet used to confirm whetherthe image forming apparatus 500 is connected to the network 530 throughthe server network interface 555. Upon receiving no response to theconfirmation packet from the image forming apparatus 500 after apredetermined time, the server controller 565 may read an IP addresspreviously allocated to the image forming apparatus 500 from the serverstorage unit 560 and may transmit the read IP address to the imageforming apparatus 500. In this embodiment, the predetermined time maycorrespond to a timeout period and can be set to a value in a range ofabout 30 seconds to about 5 minutes according to a network environment.

The DHCP server 550 may attempt to confirm whether the image formingapparatus 500 is connected to the network 530 using an ARP Broadcast,ICMP, PING, etc.

FIG. 6 is a flowchart illustrating a method of allocating an IP addressto an image forming apparatus using DHCP, according to an embodiment ofthe present general inventive concept. The method of allocating an IPaddress to an image forming apparatus using DHCP will now be explainedwith reference to FIGS. 5 and 6.

The image forming apparatus, which may be a network printer deviceconstituting a DHCP client, may be connected to the network 530connected to the DHCP server 550. Of course, the DHCP client is notrestricted to such a network printer device, but also may be any deviceallocated an IP address by the DHCP server 550 using DHCP.

The image forming apparatus 500 may be allocated an IP address by theDHCP server 550 so that a user or a printer manager may register anetwork service using the allocated IP address through the network 530.

In a situation such as when the image forming apparatus 500 is turnedoff and on, and thus the image forming apparatus 500 is disconnectedfrom the network 530 and then re-connected to the network 530 andre-allocation of an IP address is required, the image forming apparatus500 may select an IP allocation mode through the user interface 505 inoperation S600. An exemplary user interface image which may be used toselect the IP allocation mode is illustrated in FIG. 4.

The image forming apparatus 500 may transmit a DHCPDISCOVER packet tothe DHCP server 550 to request the DHCP server 550 to re-allocate an IPaddress thereto in operation S610.

The DHCP server 550 may respond to the DHCPDISCOVER packet received fromthe network printer device 500. That is, the DHCP server 550 may performa selecting operation to determine the IP address to be allocated to theimage forming apparatus 500. Specifically, the DHCP server 550 maytransmit a packet to confirm whether the image forming apparatus 500 isconnected to the network 530 in order to select the IP address to beallocated to the image forming apparatus 500 in operation S620. Thispacket may be transmitted using an ICMP, PING, ARP, etc., and the DHCPserver 550 may attempt to confirm a response of the image formingapparatus 500 to the packet.

When the image forming apparatus 500 receives this confirmation packetfrom the DHCP server 550, the image forming apparatus 500 may check theIP allocation mode in operation S630 and accordingly refuse to respondto the packet in response to the IP allocation mode corresponding to theprevious IP maintenance mode in operation S640. If there is no responsefrom the image forming apparatus 500 after a predetermined time, theDHCP server 550 may read an IP address previously allocated to the imageforming apparatus 500 from the server storage unit 560 and may transmita DHCPOFFER packet to the image forming apparatus 500 to provide thepreviously allocated IP address to the image forming apparatus 500 inoperation S650. Here, the predetermined time may correspond to a timeoutperiod and can be set to a value in a range of about 30 seconds to about5 minutes according to a network environment. In this manner, the imageforming apparatus 500 can continue to use the previous IP addresswithout changing the IP address in the DHCP server environment in whichthe DHCP discover operation confirms the to-be-allocated IP address fromthe image forming apparatus 500.

As previously described, the image forming apparatus 500 checks the IPallocation mode in response to receiving the confirmation packet, suchas an ICMP/PING/ARP packet, from the DHCP server 550 in operation S630and responds to the received confirmation packet in response to the IPallocation mode corresponding to a new IP allocation mode in operationS660. In response to the image forming apparatus 500, the DHCP server550 selects a new IP address and transmits the DHCPOFFER packet to theimage forming apparatus 500 to provide the new IP address to the imageforming apparatus 500 in operation S670.

When the image forming apparatus 500 receives the packet to confirmwhether the image forming apparatus 500 is connected to the network 530from the DHCP server 550 in operation S620, the image forming apparatus500 may display information from the received packet to a user bydisplaying the information using, for example, a panel of the imageforming apparatus 500 or a user interlace of a host device connected tothe image forming apparatus 500.

According to the present general inventive concept, the IP address ofthe DHCP client, which may undesirably vary according to the IPallocating method and environment of the DHCP server, can becontinuously maintained to improve user convenience of the DHCP clientsuch as a network printer.

The present general inventive concept may be applicable to variousclients used in a network that distributes IP addresses, such as anetwork using DHCP to distribute the IP addresses. Furthermore, thepresent general inventive concept may be useful to client IP allocationthat transmits a confirmation packet, such as, for example, anon-standard ICMP/PING/ARP packet, to confirm a DHCP client through awired/wireless network.

The present inventive concept can also be embodied as computer readablecodes on a computer readable recording medium. The computer-readablemedium may include a computer-readable recording medium and acomputer-readable transmission medium. The computer-readable recordingmedium may be any data storage device that can store data as a programwhich can be thereafter read by a computer system. Examples of thecomputer-readable recording medium include read-only memory (ROM),random-access memory (RAM), CD-ROMs, DVDs, magnetic tapes, floppy disks,and optical data storage devices. The computer-readable recording mediumcan also be distributed over network coupled computer systems so thatthe computer-readable code is stored and executed in a distributedfashion. The computer-readable transmission medium can be transmittedthrough carrier waves or signals (e.g., wired or wireless datatransmission through the Internet). Also, functional programs, codes,and code segments to accomplish the present general inventive conceptcan be easily construed by programmers skilled in the art to which thepresent general inventive concept pertains.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

What is claimed is:
 1. A method of allocating an IP address of an imageforming apparatus using Dynamic Host Configuration Protocol (DHCP),comprising: requesting a DHCP server to allocate an IP address to animage forming apparatus having a previously allocated IP address whereinthe requesting is performed by the image forming apparatus, in responseto the image forming apparatus being re-connected to a network;responding to the IP address allocation request wherein the respondingis performed by the DHCP server; checking an IP allocation mode set forthe image forming apparatus; determining, by the image formingapparatus, whether to respond to the response of the DHCP serveraccording to the checked IP allocation mode; and providing, by the DHCPserver, the previously allocated IP address to the image formingapparatus when a response is not received from the image formingapparatus in a predetermined time, or a new IP address to the imageforming apparatus when a response is received from the image formingapparatus.
 2. The method of claim 1, wherein the re-connection of theimage forming apparatus to the network comprises a power off/on of theimage forming apparatus, a network disconnection/re-connection betweenthe image forming apparatus and the DHCP server, or a combinationthereof.
 3. The method of claim 1, wherein the responding of the DHCPserver comprises transmitting a connection confirmation packet in orderto determine an IP address to be allocated to the image formingapparatus.
 4. The method of claim 3, wherein the connection confirmationpacket comprises a non-standard packet.
 5. The method of claim 4,wherein the non-standard packet comprises an Address Resolution Protocol(ARP) Broadcast, Internet Control Message Protocol (ICMP), or PING. 6.The method of claim 1, further comprising displaying the response of theDHCP server wherein the displaying is performed by the image formingapparatus.
 7. The method of claim 6, wherein the response is displayedthrough a panel of the image forming apparatus or a user interface of ahost device connected to the image forming apparatus.
 8. The method ofclaim 1, further comprising inputting the IP allocation mode ofdetermining whether the previously allocated IP address is to bemaintained in an IP allocation process using the DHCP server.
 9. Themethod of claim 8, wherein the IP allocation mode comprises a new IPallocation mode of replying to the response of the DHCP server to beallocated a new IP address and a previous IP maintenance mode ofdeclining to respond to the DHCP server to maintain the previouslyallocated IP address.
 10. An image forming apparatus comprising: astorage unit to store an IP address previously allocated by a DynamicHost Configuration Protocol (DHCP) server; a network interface totransmit/receive packets to/from the DHCP server used in IP addressallocation through a network; and a controller to request the DHCPserver to allocate an IP address through the network interface inresponse to the image forming apparatus being re-connected to thenetwork, receive a packet to confirm whether the image forming apparatusis connected to the network from the DHCP server through the networkinterface, check an IP allocation mode set for the image formingapparatus, determine whether to respond to the response of the DHCPserver according to the checked IP allocation mode, and receive thepreviously allocated IP address or a new IP address according to thechecked IP allocation mode.
 11. The image forming apparatus of claim 10,wherein the confirmation of connection of the image forming apparatus tothe network is performed using an Address Resolution Protocol (ARP)Broadcast, Internet Control Message Protocol (ICMP), or PING.
 12. Theimage forming apparatus of claim 10, further comprising a user interfaceto provide the IP allocation mode of selecting whether the previouslyallocated IP address is to be maintained in an IP allocation processusing the DHCP server.
 13. The image forming apparatus of claim 12,wherein the IP allocation mode comprises a new IP allocation mode ofreplying to the response of the DHCP server to be allocated a new IPaddress and a previous IP maintenance mode of declining to respond tothe DHCP server to maintain the previously allocated IP address.
 14. Theimage forming apparatus of claim 10, wherein the re-connection of theimage forming apparatus to the network comprises a power off/on of theimage forming apparatus, a network disconnection/re-connection betweenthe image forming apparatus and the DHCP server, or a combinationthereof.
 15. An IP allocation system using Dynamic Host ConfigurationProtocol (DHCP), comprising: an image forming apparatus to operate as aDHCP client; and a network managed by at least one DHCP server; whereinthe at least one DHCP server allocates an IP address to at least oneDHCP client comprising the image forming apparatus through the networkusing DHCP, the image forming apparatus comprises: a storage unit tostore an IP address previously allocated by the at least one DHCPserver, a network interface to transmit/receive packets to/from the atleast one DHCP server used in IP allocation through the network, and acontroller to request the at least one DHCP server to allocate the IPaddress through the network interface in response to the image formingapparatus being re-connected to the network, receive a packet to confirmwhether the image forming apparatus is connected to the network from theat least one DHCP server through the network interface, check an IPallocation mode set for the image forming apparatus, determine whetherto respond to the response of the DHCP server according to the checkedIP allocation mode, and receive the previously allocated IP address or anew IP address according to the checked IP allocation mode; and the atleast one DHCP server comprises: a server storage unit to store a rangeof IP addresses to be allocated to DHCP clients and a lease listincluding IP addresses that have been allocated to the DHCP clients andMAC addresses of the DHCP clients, which correspond to the IP addresses,a server network interface to transmit/receive packets to/from the DHCPclients used in IP allocation through the network, and a controller toreceive the IP address allocation request from the image formingapparatus through the server network interface, transmit the packet toconfirm whether the image forming apparatus is connected to the networkto the image forming apparatus, read the previously allocated IP addressof the image forming apparatus from the server storage unit and transmitthe read previously allocated IP address to the image forming apparatuswhen a response is not received from the image forming apparatus, ortransmit a new IP address to the image forming apparatus when a responseis received from the image forming apparatus.
 16. The IP allocationsystem of claim 15, wherein the confirmation of connection of the imageforming apparatus to the network is performed using an AddressResolution Protocol (ARP) Broadcast, Internet Control Message Protocol(ICMP), or PING.
 17. The IP allocation system of claim 15, wherein theimage forming apparatus further comprises a user interface to providethe IP allocation mode of selecting whether the previously allocated IPaddress is to be maintained in an IP allocation process using the DHCPserver.
 18. The method of claim 1, wherein the determining whether torespond comprises: declining to respond to the response of the DHCPserver when the checked IP allocation mode is a previous IP maintenancemode, or responding to the response of the DHCP server when the checkedIP allocation mode is a new IP allocation mode.
 19. The image formingapparatus of claim 10, wherein the controller declines to respond to theresponse of the DHCP server when the checked IP allocation mode is aprevious IP maintenance mode, or responding to the response of the DHCPserver when the checked IP allocation mode is a new IP allocation mode.